Shallow trench isolation recess process flow for vertical field effect transistor fabrication

ABSTRACT

A semiconductor device includes structures formed in first and second regions of a semiconductor substrate. The structures in the first region are spaced with a pitch P. The first and second regions are separated by an isolation region with spacing S, wherein S is greater than P. A first insulating layer is deposited and recessed to a target depth in the first region, and to a second depth in the isolation region. The second depth is lower than the target depth. A first etch stop layer is formed over the recessed first insulating layer, and a second insulating layer is formed over the first etch stop layer to increase a level of insulating material in the isolation region to the same target depth in the first device region. The recessed first insulating layer, first etch stop layer, and second insulating layer form a uniform thickness shallow trench isolation layer.

TECHNICAL FIELD

This disclosure relates generally to semiconductor fabricationtechniques and, in particular, to structures and methods for fabricatingshallow trench isolation structures for semiconductor integrated circuitdevices.

BACKGROUND

A shallow trench isolation (STI) structure comprises insulating materialwhich is deposited and patterned on a semiconductor substrate toelectrically insulate active components that are formed as part of aFEOL (front-end-of-line) layer on an active surface of the semiconductorsubstrate. A STI structure is designed to prevent or reduce the flow ofleakage current into the semiconductor substrate and to prevent othertypes of electrical interactions between active devices and components.Semiconductor fabrication process flows typically implement a STI recessprocess in which an upper surface of a STI layer is recessed beforefurther processing can take place. In semiconductor devices wheredifferent patterns of device structures are formed on the semiconductorsubstrate, recessing the STI layer to a target level is a challengingprocess because the recess level of the STI layer can vary over thesurface of the semiconductor substrate depending on the pattern densityof structures in different regions. In particular, the recess level in agiven region is dependent on the pattern density of the structures andthe amount of space (e.g., pitch) between the structures in the givenregion. The variation in recess level of a STI layer is due tomicro-loading effects of conventional etch processes whereby the STIlayer is recessed deeper in regions of the semiconductor substratehaving relaxed-pitch structure patterns as compared to regions of thesemiconductor substrate having tight-pitch structure patterns. Thus, itis a difficult and non-trivial process to uniformly recess (or etchback) a STI layer on a semiconductor substrate having differentdensities of structure patterns. The non-uniform recess of a STI layerdue to loading effects of conventional etch processes can result inundesired variation in device dimensions, which leads to undesiredvariation in device performance.

SUMMARY

Embodiments of the invention include methods for fabricating uniformthickness shallow trench isolation layers as part of a process flow forfabricating vertical FET devices, as well as semiconductor devicescomprising shallow trench isolating layers with uniform thickness.

One embodiment of the invention includes a method for fabricating asemiconductor device. The method comprises: forming semiconductor devicestructures in a first device region of a semiconductor substrate,wherein the semiconductor structures in the first device region arespaced apart at a pitch P; forming semiconductor device structures in asecond device region of the semiconductor substrate, wherein the firstand second device regions are separated by an isolation region with aspacing S, wherein S is greater than P; forming a first insulating layerover the semiconductor structures in the first and second deviceregions; recessing the first insulating layer to a target depth in thefirst device region, wherein recessing the first insulating layerresults in recessing a portion of the first insulating layer in theisolation region between the first and second device region to a depththat is lower than the target depth; forming a first etch stop layerover the recessed first insulating layer; depositing a second insulatinglayer over the first etch stop layer in the first and second deviceregions to increase a level of insulating material in the isolationregion to the target depth of the first insulating layer in the firstdevice region; and patterning the second insulating layer to form auniform thickness shallow trench isolation layer which comprises therecessed first insulating layer, a portion of the first etch stop layer,and the patterned second insulating layer.

Another embodiment of the invention includes a semiconductor device. Thesemiconductor device comprises semiconductor device structures formed ina first device region of a semiconductor substrate and semiconductorstructures formed in a second device region of the semiconductorsubstrate. The semiconductor structures in the first device region arespaced apart at a pitch P, and the first and second device regions areseparated by an isolation region with a spacing S, wherein S is greaterthan P. The device further comprises a first insulating layer formedover the semiconductor structures in the first and second deviceregions, wherein the first insulating layer is recessed to a targetdepth in the first device region, and recessed to a second depth in theisolation region between the first and second device region, wherein thesecond depth is lower than the target depth. The device furthercomprises a first etch stop layer formed over the recessed firstinsulating layer, and a second insulating layer formed over the firstetch stop layer in the first and second device regions. The secondinsulating layer increases a level of insulating material in theisolation region to the target depth of the first insulating layer inthe first device region. The recessed first insulating layer, the firstetch stop layer, and the second insulating layer collectively form auniform thickness shallow trench isolation layer.

Other embodiments will be described in the following detaileddescription of embodiments, which is to be read in conjunction with theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional side view of a semiconductordevice comprising a uniform thickness shallow trench isolation layer forvertical FET devices, according to an embodiment of the invention.

FIGS. 2 through 15 schematically illustrate a method for fabricating thesemiconductor device of FIG. 1 according to an embodiment of theinvention, wherein:

FIG. 2 is a cross-sectional schematic side view of the semiconductordevice at an intermediate stage of fabrication in which layer ofdielectric material is formed on a semiconductor substrate;

FIG. 3 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 2 after patterning the layer of dielectric material toform a first hard mask which is used to etch the semiconductorsubstrate;

FIGS. 4A and 4B are schematic views of the semiconductor structure ofFIG. 3 after patterning the semiconductor substrate using the first hardmask to form plate structures in a first device region and a seconddevice region;

FIGS. 5A and 5B are schematic views of the semiconductor structure ofFIGS. 4A and 4B after removing the first hard mask, depositing a firstlayer of insulating material over the semiconductor structure, andplanarizing the first layer of insulating material down to an uppersurface of the plate structures;

FIG. 6 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 5A after forming a layer of semiconductor materialover the planarized surface of the semiconductor structure, anddepositing and patterning a layer of dielectric material to form asecond hard mask which is used to etch the layer of semiconductormaterial;

FIGS. 7A and 7B are schematic views of the semiconductor structure ofFIG. 6 after etching the layer of semiconductor material to formvertical semiconductor fins on the plate structures in the first andsecond device regions;

FIG. 8 is a cross-sectional schematic side view of the semiconductorstructure of FIGS. 7A and 7B after depositing and planarizing a secondlayer of insulating material down to the second hard mask;

FIG. 9 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 8 after recessing the first and second layers ofinsulating material down to a target depth below the plate structures;

FIG. 10 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 9 after depositing a layer of insulating material toform a first etch stop layer;

FIG. 11 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 10 after depositing a third layer of insulatingmaterial to increase a thickness of the insulating material in isolationregions adjacent to the first and second device regions R1 and R2 to thetarget depth below upper surfaces of the plate structures;

FIG. 12 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 11 after depositing a layer of insulating material toform a second etch stop layer;

FIG. 13 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 12 after planarizing the surface of the semiconductorstructure down to the first etch stop layer on the upper regions of thevertical semiconductor fins;

FIG. 14 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 13 after recessing exposed portions of the thirdinsulating layer down to the second etch stop layer; and

FIG. 15 is a cross-sectional schematic side view of the semiconductorstructure of FIG. 14 after recessing exposed portions of the first andsecond etch stop layers down to the upper surfaces of the first andthird layers of insulating material.

DETAILED DESCRIPTION

Embodiments of the invention will now be described with regard methodsfor fabricating uniform thickness shallow trench isolation layers aspart of a process flow for fabricating vertical FET devices, as well assemiconductor devices comprising shallow trench isolating layers withuniform thickness. As explained in further detail below, embodiments ofthe invention provide methods to resolve non-uniform STI recessing whichcan result in devices regions with different feature pattern densitiesdue to micro-loading effects when etching down a layer of insulatingmaterial in the device regions with different feature pattern densities.

It is to be understood that the various layers, structures, and regionsshown in the accompanying drawings are schematic illustrations that arenot drawn to scale. In addition, for ease of explanation, one or morelayers, structures, and regions of a type commonly used to formsemiconductor devices or structures may not be explicitly shown in agiven drawing. This does not imply that any layers, structures, andregions not explicitly shown are omitted from the actual semiconductorstructures. Furthermore, it is to be understood that the embodimentsdiscussed herein are not limited to the particular materials, features,and processing steps shown and described herein. In particular, withrespect to semiconductor processing steps, it is to be emphasized thatthe descriptions provided herein are not intended to encompass all ofthe processing steps that may be required to form a functionalsemiconductor integrated circuit device. Rather, certain processingsteps that are commonly used in forming semiconductor devices, such as,for example, wet cleaning and annealing steps, are purposefully notdescribed herein for economy of description.

Moreover, the same or similar reference numbers are used throughout thedrawings to denote the same or similar features, elements, orstructures, and thus, a detailed explanation of the same or similarfeatures, elements, or structures will not be repeated for each of thedrawings. It is to be understood that the terms “about” or“substantially” as used herein with regard to thicknesses, widths,percentages, ranges, etc., are meant to denote being close orapproximate to, but not exactly. For example, the term “about” or“substantially” as used herein implies that a small margin of error ispresent, such as 1% or less than the stated amount. Further, the term“vertical” or “vertical direction” or “vertical height” as used hereindenotes a Z-direction of the Cartesian coordinates shown in thedrawings, and the terms “horizontal,” or “horizontal direction,” or“lateral direction” as used herein denotes an X-direction and/orY-direction of the Cartesian coordinates shown in the drawings.

FIG. 1 is a schematic cross-sectional side view of a semiconductordevice 100 comprising a uniform thickness shallow trench isolation layerfor vertical FET devices, according to an embodiment of the invention.The semiconductor device 100 comprises a semiconductor substrate 110,and a STI layer 112 which comprises a first insulating layer 114, asecond insulating layer 116 (alternatively referred to as etch stoplayer), and a third insulating layer 118. The semiconductor device 100further comprises a plurality of plate structures 120 and verticalsemiconductor fins 130 formed in a first device region R1, and a singleplate structure 122 and vertical semiconductor fins 132 formed in asecond device region R2. In one embodiment, the plate structures 120 and122 are formed by patterning a surface of the semiconductor substrate110.

The first device region R1 of the semiconductor device 100 furthercomprises lower source/drain regions 140, a lower insulating spacer 150,a metal gate structure 160, an upper insulating spacer 170, and uppersource/drain regions 180. The second device region R2 of thesemiconductor device 100 further comprises a lower source/drain region142, a lower insulating spacer 152, a metal gate structure 162, an upperinsulating spacer 172, and an upper source/drain region 182. It is to beunderstood that the term “source/drain region” as used herein means thata given source/drain region can be either a source region or a drainregion, depending on the application or circuit configuration.

In the example embodiment of FIG. 1, the first device region R1comprises three separate vertical FET devices T1, T2, and T3, whereineach vertical FET device T1, T2, and T3 is formed on a separate platestructure 120, and wherein each vertical FET device T1, T2, and T3comprises a corresponding lower source/drain region 140, verticalsemiconductor fin 130, and upper source/drain region 180. The verticalFET devices T1, T2, and T3 in the first device region R1 commonly sharethe metal gate structure 160. Moreover, in the example embodiment ofFIG. 1, the second device region R2 comprises a single, multi-finvertical FET device T4 which comprises three vertical semiconductor fins132 formed on the single plate structure 122, wherein the three verticalsemiconductor fins 132 are commonly connected to the lower source/drainregion 152, the upper source/drain region 182, and the metal gatestructure 162. In this configuration, the three vertical semiconductorfins 132 comprise three channel segments which are connected in parallelvia the lower and upper source/drain regions 142 and 182 to collectivelyform the single, multi-fin vertical FET device T4. As further shown inFIG. 1, the vertical FET devices T1, T2, T3, and T4 are embedded in alayer of insulating material 190 (e.g., a PMD (pre-metal dielectric)layer).

As shown in FIG. 1, the STI layer 112 comprises a uniform thickness overthe first and second device regions R1 and R2, wherein an upper surfaceof the STI layer 112 is uniformly recessed to a target depth D1 below anupper surface of the plate structures 120 and 122 in the first andsecond device regions R1 and R2. In the example embodiment of FIG. 1,the lower source/drain regions 140 are epitaxially grown on upperportions of the plate structures 120 which are exposed by the STI layer112, and the lower source/drain region 142 is epitaxially grown on anupper portion of the plate structure 122 which is exposed by the STIlayer 112. In this regard, the thickness of the recessed STI layer 112defines the active height (e.g., D1) of the upper portion of the platestructures 120 and 122 on which the lower source/drain regions 140 and142 are epitaxially grown.

In the example embodiment of FIG. 1, it is desirable to ensure that therecess level D1 of the STI layer 112 is uniform over the first andsecond device regions R1 and R2 so that the lower source/drain regions140 and 142, which are formed on the exposed upper portions of the platestructures 120 and 122, can be formed with uniform dimensions (e.g.,same height on exposed upper sidewall surfaces of the plate structures120 and 122). In conventional process flows, the deposition and etchback of a single layer of insulating material over the plate structures120/122 and vertical semiconductor fins 130/132 would result in anon-uniform recess of the single layer of insulating material due tomicro-loading effects, as the tighter pitch density of the individualstacked plate/vertical fin structures 120/130 would result in adifferent recess depth of the insulating material in the regions betweenadjacent stacked plate/vertical fin structures 122/132, as compared toother regions which have a more relaxed pitch density of patternedfeatures (see, e.g., FIG. 9). In one example embodiment of theinvention, the STI layer 112 is formed with multiple layers ofinsulating material (114, 116, 118) which are deposited and patternedusing a process flow that enables the formation of the uniformly thickSTI layer 112 as shown in FIG. 1.

Methods for fabricating the semiconductor device 100 shown in FIG. 1will now be discussed in further detail with reference to FIG. 2 throughFIG. 15, which schematically illustrate the semiconductor device 100 atvarious stages of fabrication. To begin, FIG. 2 is a cross-sectionalschematic side view of the semiconductor device at an intermediate stageof fabrication in which a layer of dielectric material 111 is formed ona semiconductor substrate 110. While the semiconductor substrate 110 isgenerically illustrated in FIG. 2, the semiconductor substrate 110 maycomprise one of different types of semiconductor substrate structures.For example, in one embodiment, the semiconductor substrate 110 maycomprise a bulk semiconductor substrate formed of, e.g., silicon, orother types of semiconductor substrate materials that are commonly usedin bulk semiconductor fabrication processes such as germanium,silicon-germanium alloy, silicon carbide, silicon-germanium carbidealloy, or compound semiconductor materials (e.g. III-V and II-VI).Non-limiting examples of compound semiconductor materials includegallium arsenide, indium arsenide, and indium phosphide. In anotherembodiment, the semiconductor substrate 110 may comprise a SOI (siliconon insulator) substrate, which comprises an insulating layer (e.g.,oxide layer) disposed between a base substrate layer (e.g., siliconsubstrate) and an active semiconductor layer (e.g., silicon layer, SiGelayer, III-V compound semiconductor layer, etc.) in which active circuitcomponents (e.g., vertical FET devices) are formed as part of a FEOLlayer.

The layer of dielectric material 111 comprises silicon nitride (SiN) orany other dielectric material that is suitable for use of etch hardmask. A next step in the illustrative fabrication process comprisespatterning the layer of dielectric material 111 to form a first hardmask that is used to etch a pattern of plate structures in the surfaceof the semiconductor substrate 110. For example, FIG. 3 is across-sectional schematic side view of the semiconductor structure ofFIG. 2 after patterning the layer of dielectric material 111 to form afirst hard mask 111-1. The layer of dielectric material 111 can bepatterned using standard photolithography techniques. For example, alayer of photoresist material is deposited on top of the layer ofdielectric material 111 and lithographically patterned (exposed anddeveloped) to form a photoresist mask having a target pattern which isto be transferred to the layer of dielectric material 111. An etchprocess is then performed using the photoresist mask to etch exposedportions of the layer of dielectric material 111 down to the surface ofthe semiconductor substrate 110 and thereby form the first hard mask111-1. The etch process can be performed using a dry etch process suchas RIE (reactive ion etching) or other etch processes with etchingchemistries that are suitable to etch the layer of dielectric material111.

FIGS. 4A and 4B schematically illustrate the semiconductor structure ofFIG. 3 after patterning the semiconductor substrate 110 using the firsthard mask 111-1 to form the plate structures 120 and 122 in the firstand second device regions R1 and R2, respectively. FIG. 4B is aschematic top plan view of the semiconductor structure of FIG. 4A, andFIG. 4A is a cross-sectional view of the semiconductor structure alongline 4A-4A in FIG. 4B. The semiconductor substrate 110 can be etchedusing a directional RIE etch (anisotropic etch) with an etch chemistrythat is suitable to etch the semiconductor material of the semiconductorsubstrate 110 selective to the first hard mask 111-1. As shown in FIGS.4A and 4B, the plate structures 120 in the first device region R1 areformed with a width W1, height H1, and length L1, and are spaced by adistance S1. Further, the plate structure 122 in the second deviceregion R2 is formed to have a width W2, which is greater than W1. Theplate structure 122 has a height H1 and length L1 which is the same asthe plate structures 120 in the first device region R1. In one exampleembodiment, the width W1 is in a range of about 10 nm to about 20 nm,the width W2 is in a range of about 100 nm to about 200 nm, the heightH1 is in a range of about 30 nm to about 100 nm, and the length L1 is ina range of about 50 nm to about 1000 nm.

FIGS. 5A and 5B are schematic views of the semiconductor structure ofFIGS. 4A and 4B after removing the first hard mask 111-1, depositing afirst layer of insulating material 114-1 over the semiconductorstructure, and planarizing the first layer of insulating material 114-1down to an upper surface of the plate structures 120 and 122. FIG. 5B isa schematic top plan view of the semiconductor structure of FIG. 5A, andFIG. 5A is a cross-sectional view of the semiconductor structure alongline 5A-5A in FIG. 5B. The first layer of insulating material 114-1 maycomprise any suitable dielectric material that is commonly utilized inFEOL process technologies including, but not limited to, silicon oxide(e.g. SiO₂), silicon nitride (e.g., (Si₃N₄), hydrogenated silicon carbonoxide (SiCOH), SiCH, SiCNH, or other types of silicon-based low-kdielectrics (e.g., k less than about 4.0), porous dielectrics, or knownULK (ultra-low-k) dielectric materials (with k less than about 2.5). Thefirst insulating layer 114-1 may be deposited using known depositiontechniques, such as, for example, ALD (atomic layer deposition), CVD(chemical vapor deposition) PECVD (plasma-enhanced CVD), or PVD(physical vapor deposition), or spin-on deposition.

A next phase of the semiconductor fabrication process comprises formingvertical semiconductor fins on the plate structures 120 and 122 using aprocess flow as schematically illustrated in FIGS. 6, 7A, and 7B. Inparticular, FIG. 6 is a cross-sectional schematic side view of thesemiconductor structure of FIG. 5A after forming a layer ofsemiconductor material 130A over the planarized surface of thesemiconductor structure, and depositing and patterning a layer ofdielectric material (e.g., SiN) to form a second hard mask 111-2 whichis used to etch the layer of semiconductor material 130A to formvertical semiconductor fins. The layer of semiconductor material 130Amay comprise a crystalline silicon material, or other types ofsemiconductor materials that are commonly used to form verticalsemiconductor fins for vertical FET devices such as germanium, asilicon-germanium alloy, a compound semiconductor material (e.g. III-Vmaterial), etc. The layer of semiconductor material 130A can bedeposited or epitaxially grown using known methods such as CVD, MOCVD(metal-organic CVD), LPCVD (Low Pressure CVD), MBE (molecular beamepitaxy), VPE (vapor-phase epitaxy), or other known epitaxial growthtechniques which are suitable for the given process flow. In oneembodiment, the layer of semiconductor material 130A is formed with athickness (denoted H2 in FIG. 6) in a range of about 50 nm to about 100nm, wherein the thickness of the layer of semiconductor material 130Adefines a height (H2) of the vertical semiconductor fins subsequentlyformed on the plate structures 120 and 122.

Next, FIGS. 7A and 7B are schematic views of the semiconductor structureof FIG. 6 after forming the vertical semiconductor fins 130 and 132 onthe plate structures 120 and 122, respectively, in the first and seconddevice regions R1 and R2. FIG. 7A is a schematic cross-sectional view ofthe semiconductor structure along line 7A-7A in FIG. 7B, and FIG. 7B isa schematic top plan view of the semiconductor structure along line7B-7B in FIG. 7A. The vertical semiconductor fins 130 and 132 can beformed by anisotropically etching the layer of semiconductor material130A with a dry etch plasma process (e.g., RIE) with an etch chemistrythat is suitable to etch the layer of semiconductor material 130Aselective to the material of the second hard mask 111-2. As shown inFIGS. 7A and 7B, the vertical semiconductor fins 130 and 132 are formedwith a width W2 and length L2, which are slightly less than the width W1and length L1 dimensions of the plate structures 120 and 122. Thevertical semiconductor fins 130 and 132 are formed with a height H2,which is defined by the thickness of the layer of semiconductor material130A (FIG. 6). As further shown in FIG. 7A, the individual devicestructures 120/130 are spaced apart at a pitch P, and the device regionsR1 and R2 are separated by an isolation region of distance S, wherein Pis less than S.

Next, FIG. 8 is a cross-sectional schematic side view of thesemiconductor structure of FIGS. 7A and 7B after depositing andplanarizing a second layer of insulating material 114-2 down to thesecond hard mask 111-2. In one embodiment of the invention, the secondlayer of insulating material 114-2 is formed of the same material (e.g.,silicon oxide) as the first layer of insulating material 114-1. Thefirst and second layers of insulating material 114-1 and 114-2collectively form an ILD (interlevel dielectric) layer 114-3 that isrecessed to form the first insulating layer 114 of the STI layer 112 ofthe semiconductor device 100 (FIG. 1). The second layer of insulatingmaterial 114-2 is formed to provide a planarized surface as a baselinefor a timed etch to recess the ILD layer 114-3 down to a target depth,as shown in FIG. 9.

In particular, FIG. 9 is a cross-sectional schematic side view of thesemiconductor structure of FIG. 8 after etching the ILD layer 114-3 downto a target depth D1 below the plate structures 120 in the first deviceregion R1 to form the first insulating layer 114 of the STI layer 112(FIG. 1). In one embodiment, the ILD etch process is performed using adry etch process, such as RIE, with an etch chemistry that is selectiveto the semiconductor materials of the plate structures 120 and 122, thevertical semiconductor fins 130 and 132, and the second hard mask 111-2.With this etch process, the ILD layer 114-3 is recessed down to thetarget depth D1 below the upper surfaces of the plate structures 120 inthe first device region R1, while the ILD layer 114-3 is recessed downto a lower depth D2 below the upper surfaces of the plate structures 120and 122 in the isolation regions adjacent to the first and second deviceregions R1 and R2.

In particular, as shown in FIG. 9, to achieve a target depth D1 in thefirst device region R1, the ILD layer 114-3 is recessed to the lowerdepth D2 in the isolation regions adjacent to the device regions R1 andR2 due to micro-loading effects of the RIE etch process, which causesthe ILD layer 114-3 to be recessed deeper (e.g., depth D2) in areas witha lower density of patterned features (e.g., isolation region ofdistance S between the adjacent plate structures 120 and 122), ascompared to the shallower recess depth (e.g., depth D1) which results inareas with higher density (smaller pitch) of patterned features (e.g.,spaces between adjacent plate/vertical fin structures 120/130). Incertain instances, a differential depth D between the recessed depths D2and D1 can be in a range of 30 nm to 40 nm. This variation in recessdepth of the ILD layer 114-3 results in the formation of the firstinsulating layer 114 of the STI layer with a non-uniform thickness(e.g., portions of the first insulating layer 114 between adjacent platestructures 120 are thicker than portions of the first insulating layer114 adjacent to the device regions R1 and R2).

As a result of the non-uniform thickness of the first insulating layer114, the amount of exposure of the upper sidewalls of the platestructures 120 and 122 varies, which is undesirable for forming thelower epitaxial source/drain regions on the upper regions of the platestructures 120 and 122. Indeed, if the first insulating layer 114 shownin FIG. 9 was utilized as the STI layer, the size of the lowersource/drain regions 140 and 142 grown on the exposed upper portions ofthe plate structures 120 and 122 would significantly vary, as epitaxialgrowth of the semiconductor material on the exposed sidewalls of theplate structures 120 and 122, which are exposed at the depth D2, wouldbe significantly larger than the epitaxial growth of the semiconductormaterial on the exposed sidewalls of the plate structures 120, which areexposed at the shallower depth D1. In one embodiment, the process flowas schematically shown in FIGS. 10 through 15 is implemented to form auniform thickness STI layer.

As an initial step. FIG. 10 is a cross-sectional schematic side view ofthe semiconductor structure of FIG. 9 after depositing a layer ofinsulating material to form a first etch stop layer 116. In oneembodiment of the invention, the first etch stop layer 116 is formed bydepositing a conformal layer of SiN, or some other type ofinsulating/dielectric material which can be etched selective to thematerials that are used to form the insulating layers 114 and 118 of theSTI layer 112 (FIG. 1). In one embodiment, the first etch stop layer 116is formed with a thickness in a range of about 3 nm to about 5 nm. Asexplained in further detail below, the first etch stop layer 116 definesan active plate height (e.g., D1) for the subsequent formation of thelower source/drain regions 140 of the single vertical FET devices T1,T2, and T3 in the first device region R1.

Next, FIG. 11 is a cross-sectional schematic side view of thesemiconductor structure of FIG. 10 after depositing a third layer ofinsulating material 118 to increase a thickness of the insulatingmaterial in the isolation regions adjacent to the device regions R1 andR2 to the target depth D1 below the upper surfaces of the platestructures 120 and 122. In one embodiment of the invention, the thirdlayer of insulating material 118 is formed of the same material (e.g.,silicon oxide) as the first insulating layer 114, although other typesof insulating materials may be used which can be etched selective to thematerial of the first etch stop layer 116. As schematically shown inFIG. 11, the third layer of insulating material 118 is deposited torefill the isolation regions adjacent to the device regions R1 and R2with enough insulating material so that an upper surface of the layer ofinsulating material 118 in the isolation regions is increased to thesame level (or substantially the same level) as the level of the firstinsulating layer 114 between the adjacent plate structures 120 in thefirst device region R1. As a result, as shown in FIG. 11, the uppersurface of the third layer of insulating material 118 in the isolationregions adjacent to the first and second device regions R1 and R2 isincreased to the target depth D1 below the upper surfaces of platestructures 120 and 122.

As further shown in FIG. 11, deposition of the third layer of insulatingmaterial 118 results in refilling the spaces between adjacent verticalsemiconductor fins 130 in the first device region R1 with the insulatingmaterial 118, as well as refilling the spaces between adjacent verticalsemiconductor fins 132 in the second device region R2 with theinsulating material 118. During deposition of the third layer ofinsulating material 118, due to the high aspect ratio of the spacesbetween adjacent vertical semiconductor fins 130 and 132 in the deviceregions R1 and R2, the insulating material is deposited in the spacesbetween adjacent vertical semiconductor fins 130 and 132 at a fasterrate than the rate at which the insulating material is deposited in theisolation regions adjacent to the device regions R1 and R2, therebyresulting in the semiconductor structure shown in FIG. 11.

Next, FIG. 12 is a cross-sectional schematic side view of thesemiconductor structure of FIG. 11 after depositing a layer ofinsulating material to form a second etch stop layer 119. In oneembodiment, the second etch stop layer 119 is formed by depositing aconformal layer of SiN, or some other type of insulating/dielectricmaterial which can be etched selective to the insulating material of thethird insulating layer 118. In one embodiment, the second etch stoplayer 119 is formed with a thickness in a range of about 3 nm to about 5nm. As explained in further detail below, the second etch stop layer 119defines an active plate height (e.g., D1) for the formation of the lowersource/drain region 142 of the single, multi-fin vertical FET device T4in the second device region R2.

Following formation of the structure shown in FIG. 12, a CMP process isformed to remove overburden insulating material on the upper portions ofthe vertical semiconductor fins 130 and 132. For example, FIG. 13 is across-sectional schematic side view of the semiconductor structure ofFIG. 12 after planarizing the surface of the semiconductor structuredown to the first etch stop layer 116 on the upper regions of thevertical semiconductor fins 130 and 132. The CMP process removes theupper portions of the second etch stop layer 119 and the thirdinsulating layer 118 down to the surface of the first etch stop layer116 over the vertical semiconductor fins 130 and 132. The CMP processexposes portions of the third insulating layer 118 disposed between thevertical semiconductor fins 130 in the first device region R1 andbetween the vertical semiconductor fins 132 in the second device regionR2.

Next, FIG. 14 is a cross-sectional schematic side view of thesemiconductor structure of FIG. 13 after etching the exposed portions ofthe third insulating layer 118 between the vertical semiconductor fins130 and 132 down to the second etch stop layer 119. With this etch backprocess, the exposed portions of the third insulating layer 118 betweenthe vertical semiconductor fins 130 and 132 are etched selective to thematerials of the first and second etch stop layers 116 and 119 toprevent etching of the portions of the first and third insulating layers114 and 118 which define the STI layer 112.

Following the etch back of the insulating material 118 disposed betweenthe vertical semiconductor fins 130 and 132, another etch process isperformed to remove the exposed portions of the first and second etchstop layers 116 and 119 selective to the insulating materials of thefirst and third insulating layers 114 and 118. In particular, FIG. 15 isa cross-sectional schematic side view of the semiconductor structure ofFIG. 14 after recessing the exposed portions of the first and secondetch stop layers 116 and 119 down to the first and third insulatinglayers 114 ad 118. With this process, the second etch stop layer 119 iscompletely removed, while a portion of the first etch stop layer 116remains embedded between the first and third insulating layers 114 and118 of the STI layer 112. The resulting structure shown in FIG. 15comprises a uniform thickness STI layer 112, which is uniformly recessedto define uniform plate heights (e.g., D1) for epitaxially growinguniform source/drain regions on the upper surfaces of the platestructures 120 and 122.

Following the formation of the semiconductor structure shown in FIG. 15,any known sequence of processing steps can be implemented to completethe fabrication the semiconductor integrated circuit device as shown inFIG. 1, the details of which are not needed to understand embodiments ofthe invention. Briefly, by way of example, referring back to FIG. 1,FEOL processing can continue by forming the lower source/drain regions140 and 142 on the upper surfaces of the plate structures 120 and 122.In one embodiment, lower source/drain regions 140 and 142 are formed byepitaxially growing doped semiconductor layers (e.g., doped SiGe) on theexposed upper portions of the plate structures 120 and 122 using knownselective growth techniques in which epitaxial material is notselectively grown on the exposed surfaces of STI layer 112. The type ofepitaxial semiconductor material that is used to form the lowersource/drain regions 140 and 142 will vary depending on various factorsincluding, but are not limited to, the type of material of the verticalsemiconductor fins 130 and 132, the device type (e.g., n-type or p-type)of the vertical FET devices T1, T2, T3, and T4 in the device regions R1and R2, etc.

Prior to formation of the lower source/drain regions 140 and 142, thinlayer of gate dielectric can be deposited and patterned to form a gatedielectric layer on the sidewalls of the vertical semiconductor fins 130and 132. The lower source/drain regions 140 and 142 may be in-situ dopedduring epitaxial growth by adding a dopant gas to the source depositiongas (i.e., the Si-containing gas). Exemplary dopant gases may include aboron-containing gas such as BH₃ for pFETs or a phosphorus or arseniccontaining gas such as PH₃ or AsH₃ for nFETs, wherein the concentrationof impurity in the gas phase determines its concentration in thedeposited film. Alternatively, the source/drain regions 140 and 142 canbe doped ex-situ by ion implantation.

The lower insulating spacers 150 and 152 are then formed by depositingand patterning a layer of insulating material such as SiN, which can beetched selective to the insulating layer 118 of the STI layer 112. Themetal gate structures 160 and 162 are formed by depositing andpatterning one or more layers of metallic material (e.g., depositing aconformal work function metal layer on a gate dielectric layer, and agate electrode layer on the conformal work function metal). The lowerinsulating spacers 150 and 152 serve to electrically insulate the lowersource/drain regions 140 and 142 from the metal gate structures 160 and162.

The upper insulating spacers 170 and 172 are formed be depositing andpatterning a layer of insulating layer on the upper surface of the metalgate structures 160 and 162. The upper source/drain regions 180 and 182are epitaxially grown on exposed upper portions of the verticalsemiconductor fins 130 and 132. The upper source/drain regions 180 and182 are electrically insulated from the metal gate structures 160 and162 by the upper insulating spacers 170 and 172. One or more layers ofinsulating material are then deposited to form the PMD layer 190, whichencapsulates the vertical FET devices T1, T2, T3 and T4 in insulatingmaterial. Thereafter, processing can continue to form one or moreadditional PMD layers over the semiconductor structure shown in FIG. 1and then form vertical device contacts in the insulating layers (e.g.,PMD layer 190) to the upper and lower source/drain regions 140, 142,180, 182, and the metal gate structures 160 and 162 using knowntechniques and materials. Following formation of the device contacts, aBEOL (back end of line) interconnect structure is formed to provideconnections to/between the vertical FET devices T1, T2, T3 and T4 andother active or passive devices that are formed as part of the FEOLlayer.

It is to be understood that the methods discussed herein for fabricatinguniform thickness STI layers for vertical FET devices can beincorporated within semiconductor processing flows for fabricating othertypes of semiconductor devices and integrated circuits with variousanalog and digital circuitry or mixed-signal circuitry. In particular,integrated circuit dies can be fabricated with various devices such asfield-effect transistors, bipolar transistors, metal-oxide-semiconductortransistors, diodes, capacitors, inductors, etc. An integrated circuitin accordance with the present invention can be employed inapplications, hardware, and/or electronic systems. Suitable hardware andsystems for implementing the invention may include, but are not limitedto, personal computers, communication networks, electronic commercesystems, portable communications devices (e.g., cell phones),solid-state media storage devices, functional circuitry, etc. Systemsand hardware incorporating such integrated circuits are considered partof the embodiments described herein. Given the teachings of theinvention provided herein, one of ordinary skill in the art will be ableto contemplate other implementations and applications of the techniquesof the invention.

Although exemplary embodiments have been described herein with referenceto the accompanying figures, it is to be understood that the inventionis not limited to those precise embodiments, and that various otherchanges and modifications may be made therein by one skilled in the artwithout departing from the scope of the appended claims.

What is claimed is:
 1. A method for fabricating a semiconductor device,comprising: forming semiconductor device structures in a first deviceregion of a semiconductor substrate, wherein the semiconductorstructures in the first device region are spaced apart at a pitch P;forming semiconductor device structures in a second device region of thesemiconductor substrate, wherein the first and second device regions areseparated by an isolation region with a spacing S, wherein S is greaterthan P; forming a first insulating layer over the semiconductorstructures in the first and second device regions; recessing the firstinsulating layer to a target depth in the first device region, whereinrecessing the first insulating layer results in recessing a portion ofthe first insulating layer in the region between the first and seconddevice region to a depth that is lower than the target depth; forming afirst etch stop layer over the recessed first insulating layer;depositing a second insulating layer over the first etch stop layer inthe first and second device regions to increase a level of insulatingmaterial in the isolation region to the target depth of the firstinsulating layer in the first device region; and patterning the secondinsulating layer to form a uniform thickness shallow trench isolationlayer which comprises the recessed first insulating layer, a portion ofthe first etch stop layer, and the patterned second insulating layer;wherein the semiconductor device structures in the first device regioncomprise a pattern of vertical semiconductor fins formed on top ofindividual plate structures, and wherein the semiconductor devicestructures in the second device region comprises a pattern of verticalsemiconductor fins formed on top of a single plate structure.
 2. Themethod of claim 1, wherein the plate structures in the first and seconddevice regions are formed by patterning a surface of the semiconductorsubstrate.
 3. The method of claim 1, wherein an upper surface of theuniform thickness shallow trench isolation layer is formed at a uniformdepth below an upper surface of each of the plate structures in thefirst and second device regions.
 4. The method of claim 3, furthercomprising epitaxially growing source/drain regions on upper portions ofthe plate structures in the first and second device regions, which areexposed above the uniform thickness shallow trench isolation layer. 5.The method of claim 1, wherein recessing the first insulating layer to atarget depth in the first device region comprises recessing the firstinsulating layer to a target depth below the upper surfaces of the platestructures in the first device region.
 6. The method of claim 5, whereindepositing the second insulating layer over the first etch stop layer inthe first and second device regions to increase the level of insulatingmaterial in the isolation region to the target depth of the firstinsulating layer in the first device region comprises depositinginsulating material over the first etch stop layer until the insulatingmaterial reaches a same target depth below the upper surface of theplate structure in the second device region as the target depth of thefirst insulating layer below the upper surfaces of the plate structuresin the first device region.
 7. A method for fabricating a semiconductordevice, comprising: forming semiconductor device structures in a firstdevice region of a semiconductor substrate, wherein the semiconductorstructures in the first device region are spaced apart at a pitch P;forming semiconductor device structures in a second device region of thesemiconductor substrate, wherein the first and second device regions areseparated by an isolation region with a spacing S, wherein S is greaterthan P; forming a first insulating layer over the semiconductorstructures in the first and second device regions; recessing the firstinsulating layer to a target depth in the first device region, whereinrecessing the first insulating layer results in recessing a portion ofthe first insulating layer in the region between the first and seconddevice region to a depth that is lower than the target depth; forming afirst etch stop layer over the recessed first insulating layer;depositing a second insulating layer over the first etch stop layer inthe first and second device regions to increase a level of insulatingmaterial in the isolation region to the target depth of the firstinsulating layer in the first device region; and patterning the secondinsulating layer to form a uniform thickness shallow trench isolationlayer which comprises the recessed first insulating layer, a portion ofthe first etch stop layer, and the patterned second insulating layer,wherein patterning the second insulating layer to form the uniformthickness shallow trench isolation layer comprises; patterning a secondetch stop layer to expose a portion of the second insulating layer to beremoved; recessing the exposed portion of the second insulating layerdown to the first etch stop layer; and etching the second etch stoplayer selective to the first and second insulating layers.
 8. The methodof claim 7, wherein etching the second etch stop layer comprisescompletely removing the second etch stop layer.
 9. The method of claim7, further comprising etching an exposed portion of the first etch stoplayer selective to the first and second insulating layers.
 10. Asemiconductor device, comprising: semiconductor device structures formedin a first device region of a semiconductor substrate, wherein thesemiconductor structures in the first device region are spaced apart ata pitch P; semiconductor device structures formed in a second deviceregion of the semiconductor substrate, wherein the first and seconddevice regions are separated by an isolation region with a spacing S,wherein S is greater than P; a first insulating layer formed over thesemiconductor structures in the first and second device regions, whereinthe first insulating layer is recessed to a target depth in the firstdevice region, and recessed to a second depth in the isolation regionbetween the first and second device region, wherein the second depth islower than the target depth; a first etch stop layer formed over therecessed first insulating layer; and a second insulating layer formedover the first etch stop layer in the first and second device regions,wherein the second insulating layer increases a level of insulatingmaterial in the isolation region to the target depth of the firstinsulating layer in the first device region; wherein the recessed firstinsulating layer, the first etch stop layer, and the second insulatinglayer collectively form a uniform thickness shallow trench isolationlayer; wherein the semiconductor device structures in the first deviceregion comprises a pattern of vertical semiconductor fins formed on topof individual plate structures, and wherein the semiconductor devicestructures in the second device region comprises a pattern of verticalsemiconductor fins formed on top of a single plate structure.
 11. Thesemiconductor device of claim 10, wherein the plate structures in thefirst and second device regions are formed by patterning a surface ofthe semiconductor substrate.
 12. The semiconductor device of claim 10,wherein an upper surface of the uniform thickness shallow trenchisolation layer is formed at a uniform depth below an upper surface ofeach of the plate structures in the first and second device regions. 13.The semiconductor device of claim 12, further comprising source/drainregions epitaxially grown on upper portions of the plate structures inthe first and second device regions, which are exposed above the uniformthickness shallow trench isolation layer.
 14. The semiconductor deviceof claim 13, further comprising: lower insulating spacers formed overthe source/drain regions in the first and second device regions; metalgate structures formed on sidewalls of the vertical semiconductor finsin the first and second device regions; upper insulating spacers formedon the metal gate structures in the first and second device regions; andupper source/drain regions formed on upper portions of the verticalsemiconductor fins in the first and second device regions.
 15. Thesemiconductor device of claim 10, wherein the first insulating layer isrecessed to the target depth in the first device region below the uppersurfaces of the plate structures in the first device region.
 16. Thesemiconductor structure of claim 15, wherein the second insulating layeris formed over the first etch stop layer in the first and second deviceregions to increase the level of insulating material in the isolationregion to a same target depth below the upper surface of the platestructure in the second device region as the target depth of the firstinsulating layer below the upper surfaces of the plate structures in thefirst device region.
 17. The semiconductor structure of claim 10,wherein the first and second insulating layers are formed of a sameinsulating material.
 18. The semiconductor device of claim 10, whereinthe semiconductor structures formed in the first and second deviceregion are components of vertical FET (field effect transistor) devices.